Interesting question Pecker, I will try to answer that as best as I can.
Well, the male testicles are outside the body because it is cooler on the outside, therefore the sperm may flourish. So, *pardon my crudeness* if I kinda let them hang away from my legs, they get cold. Like freaky cold, cold that scares me and makes me bring my legs back together.
Please pardon me for my crudeness, it seemed like the only way I could explain it.